1. Field of the Invention
This invention relates to a slider of a slide fastener comprising a slider body and a lug molded integrally by die casting, to which a pull tab is secured subsequently. It also relates to a metal mold for molding the same.
2. Prior Art
A slider of a slide fastener of the type under consideration has to be securely combined with a pull tab in a later stage of manufacturing. For securing a pull tab to the slider, a ring of the pull tab is introduced into the space between the arched lug and the slider body through the gap between a rear pillar of the lug and an upper wing of the slider body and then a front pillar of the lug is plastically deformed and bent toward the upper wing typically by means of a pincher. Thus, a slide fastener of this type can be realized by combining a slider body and a pull tab selected from a variety stocks to meet the demand of the consumer.
Meanwhile, a metal mold for producing a slider of the above identified type comprises an upper mold for defining the profile of the upper half of the upper wing and that of the lug, a lower mold for defining the profile of the lower half of the lower wing and an intermediary mold for defining the profiles of the remaining portions of the upper and lower wings and a so-called diamond section (guide post) as typically described in Japanese Utility Model Application Laid-Open No. 2-12889, of which the upper and lower molds include respective first and second (left and right) mold halves, whereas the intermediary mold includes first and second (front and rear) mold halves.
The lower mold has an U-shaped cross section with a groove formed at the center, into which the intermediary mold is placed. The first and second mold halves of the intermediary mold can slide back and forth between the upper and lower molds, whereas the first and second mold halves of the upper and lower molds can be moved laterally to open and close the mold assembly.
Known sliders of the type under consideration are accompanied by a drawback that, when the pull tab is brought into the space between the lug and the slider body and the front pillar is bent down for plastic deformation in order to securely anchor the pull tab, the front pillar can give rise to a fissure. It is very difficult to completely prevent such a fissure from taking place even if a rigorous quality control system is in place because of variations in the molded material and the molding conditions. Additionally, if the front pillar is properly deformed, there can occur a spring back phenomenon in it to produce a significant gap between the upper surface of the upper wing and the rear pillars. If the front pillar is bent downward with enhanced pressure to eliminate the gap, then not only can the front pillar be damaged but it can press to the upper surface of the upper wing at the lower end to deform the latter and damage the internal passage for the elements of the fastener and hence the commercial value of the fastener.
Meanwhile, known metal molds for molding sliders of the type under consideration comprise quite a number of components that have to be machined accurately to raise the manufacturing cost of the mold, while such a mold cannot be used for molding a large number sliders because of its durability. Additionally, each of the components is required to operate in a complex manner with timings that can be very complicated. Thus, the net result will be a high manufacturing cost of the fastener.
In view of these circumstances, it is therefore an object of the present invention to provide a quality slider for a slide fastener that is free from the above identified problems including the possible damage of the lug that can occur when the front pillar of the lug is pressed and deformed, the problem of spring back and that of a deformed upper wing and also to provide a metal mold for molding sliders of slide fasteners that has a simple structure and can be used for manufacturing a large number of sliders at low cost to improve the productivity.
According to the invention, the above objects and other objects of the invention are achieved by providing a slider for a slide fastener comprising a body including an upper wing and a lower wing linked together by a diamond section (guide post) and a lug secured to the upper surface of the upper wing. The lug is integrally molded with the body by die casting. The lug is arched and at least has a front pillar securely and integrally held to the upper surface of a front portion of the upper wing. Between the rear end of the lug and the upper surface of the upper wing, a gap is provided for allowing the ring of a corresponding pull tab to pass therethrough. There is also provided a pair of rear lateral members arranged for supporting the lug at the rear end thereof.
In a slider according to the invention, the rear lateral members of the lug may be rear lateral legs extending downward from the oppositely disposed lateral sides at the rear end of the lug. Alternatively, they may be laterally arranged rear pillars projecting upward from a central area of the rear end of the upper surface of the upper wing. Preferably, the lug has an engaging portion formed at the rear end of its main body for engagement with the top ends of the rear lateral pillars projecting upward from the upper wing.
When the rear lateral members of the lug are rear lateral legs extending downward from the oppositely disposed lateral sides at the rear end of the lug, they provide an advantage of preventing the upper wing from being deformed and damaged if the lug is subjected to strong pinching force for the above described plastic deformation; because the lateral legs are deformed firstly to absorb any excessive pinching force. More specifically, the rear lateral legs will be swerved sideways so that, once the lug springs back, they may elastically restore the original positions and their lower ends may come into contact with the upper surface of the upper wing to eliminate any gap that may have been formed between the lower ends of the legs and the upper surface of the upper wing.
When the rear lateral members of the lug are laterally arranged rear pillars projecting upward from a central area of the rear end of the upper surface of the upper wing, the elastic deformation can be minimized because the rear end of the lug does not have to be held in close contact with the top ends of the rear lateral pillars.
In a preferred mode of carrying out the invention, the lug has one or more than one ribs extending longitudinally in a central area of a lower surface thereof. The one or more than one ribs projecting downward from the lower surface of the lug operate effectively for reinforcing the front pillar and the main body of the lug. Additionally, the ribs minimize the contact area between the pull tab and the lower surface of the lug when the pull tab is pulled to scrape the lug""s lower surface and hence protect the lower longitudinal edges of the lug against being scraped off so that the pull tab may always be operated smoothly with regard to the lug.
Preferably, a longitudinal groove is formed in a central area of the upper surface with a profile matching that of the ring of the pull tab, extending from the front pillar of the lug to the rear end of the slider body. When the lug has rear lateral legs extending downward from the oppositely disposed lateral sides at the rear end of the lug, the groove serves to facilitate the operation of introducing the ring of the pull tab into the space between the arched lug and the slider body through the gap between the rear lateral lugs of the lug and the upper wing.
With a slider having the above described figure, the rear end of the lug is plastically deformed to bend toward the rear end of the upper wing in order to securely hold a pull tab in position after introducing the pull tab through a gap between the lug and the upper wing.
A slider comprising a lug as an integral part can be manufactured at low cost by means of a metal mold according to the invention and having a structure as described below.
According to the invention, there is provided a metal mold for molding a slider of a slide fastener by die casting to integrally produce a pair of oppositely disposed upper and lower wings and a lug secured to the upper surface of the upper wing. The metal mold comprises an upper mold, a lower mold and two or more sliding molds. The upper mold has a cavity for integrally molding part of the lug except the rear lateral legs and part of the upper wing to define the profile of the upper and lateral surface of the lug and part of the upper surface of the upper wing. The lower mold has a cavity for molding part of the lower wing to define the profile of the lower surface of the lower wing and adapted to move up and down in order to come into contact with the upper mold and leave the latter in an alternating manner. The two or more than two sliding molds have an internal profile adapted to mold the remaining portions of the upper and lower wings and of the lug not molded by the upper and lower molds. They are removably introduced between the closely held upper and lower molds from front and rear sides. The cavity defined by the upper mold and the sliding mold for molding the rear lateral members has a substantially inverted U-shaped cross section. In a metal mold according to the invention, the sliding mold for defining an lower surface of the lug has one or more than one rib forming grooves extending longitudinally on the upper surface thereof.
Alternatively, at least either one of the upper and lower molds may be divided into two front and rear halves, at least one of which is adapted to move back and forth. Preferably, in a metal mold according to the invention, the sliding mold has a bulged section for forming a groove in a central area of the upper surface of the upper wing with a profile matching that of the ring of the pull tab, extending from the front pillar of the lug to the rear end of the slider body so that the ring of the pull tab may be introduced with ease through the gap between the lug and the upper wing.
According to another aspect of the invention, if a metal mold according to the invention is used for molding rear lateral pillars projecting upward from the upper surface of the upper wing, the portion of the sliding mold for forming rear lateral members of the slider has a substantially T-shaped cross section.
With a metal mold according to the invention and having a structure as described above, the molding operation typically proceeds in a manner as described below. Once the molding material filled in the metal mold is set, the plurality of sliding molds are moved in predetermined respective directions and then upper and lower molds are moved upward and downward respectively to open the metal mold. Then, the slider body having a lug remains either in the upper mold or in the lower mold. Then, an eject pin is operated to project into the cavity and move out the molded product from the mold. If a number of slider bodies with lugs are simultaneously molded in a single molding process, they are separated from each other by appropriate known separation means. Finally, a pull tab is fitted to each of the slider body with a lug that may or may not have been secured to a fastener tape.